Preheat your oven to 400°F (200°C) and line a large rimmed baking sheet with parchment paper for easy cleanup.
Peel and cube the sweet potato into half-inch pieces and halve the Brussels sprouts.
Place the sweet potatoes and Brussels sprouts on the baking sheet, drizzle with 0.5 tsp of olive oil, and sprinkle with half of the sea salt, pepper, and dried oregano.
Toss the vegetables to coat evenly and spread them out in a single layer; roast in the oven for 15 minutes.
While the vegetables roast, mince the garlic and whisk it together with the remaining 0.5 tsp of olive oil and the rest of the salt, pepper, and oregano.
Remove the baking sheet from the oven, push the vegetables to the edges, and place the salmon fillet in the center.
Rub the garlic oil mixture over the top of the salmon fillet and return the pan to the oven.
Roast for an additional 10 to 12 minutes, or until the salmon is opaque and flakes easily with a fork and the vegetables are tender.
Remove from the oven and drizzle the fresh lemon juice over the salmon and vegetables before serving.